Apparatus for the continuous production of polycaproamide

ABSTRACT

An installation for the continuous production of polycaproamide comprises the following units connected in series in the order given: a unit for melting caprolactam; a unit for mixing the molten caprolactam with an activator and a stabilizer; a unit for continuous polymerization of caprolactam; a unit for distilling off low-molecular compounds; a unit for catalytic decomposition of cyclic oligomers of caprolactam; and a unit for condensation of low-molecular compounds.

inventors Boris Alanasievich Kharkov tposelok Khiminstituta, 4, kv. 22,Kalinin;

losli Zalmanovich Kunin, poselok, Khlmlnstituta, 2, kv. 5, Kalinin;Vladimir Nikolaevich Skufiin, prospekt Pobedy, 25, kv. 7, Kalinin; GlebKonstantinovich Moiseev, poselok Khiminstituta, 10, kv. 4, Kalinin;Vladimir Nikolaevich Vysotsky, poselok Khiminstituta, 3, kv. l, Kalinin;Vladimir Kuzmich Muraviev, poselok Khiminstituta, 6, kv. 27, Kalinin;Avgust Alexandrovich Dubynin, Moskovskoi oblasti, Borodinsky proezd, 30,kv. 59, Klin; Vladimir Mikhailovich Kharitonov, poselok Khiminstituta,10, kv. 6, Kalinin; Alexandr Anatolievich Speransky, poselokKhiminstituta, 3, kv. 20, Kalinin; Vsevolod Pavlovich Junitsky, ulitsaPravdy, 37, kv. l7, Kalinin; Evgeny Mikhailovich Kozlov, poselokKhiminstituta, 9, kv. 16, Kalinin; Evgeny Anatolievich Gryaznov, poselokKhiminstituta, 2, kv. 34, Kalinin, U.S.S.R.; Valery Tikhonovich Bykov,poselok Khiminstituta, 3, kv. 43, Kalinin; Erick Georgievich Podushkin,poselok Khiminstituta, 9, kv. 24, Kalinin; Vladimir YakovlevichStreitses, poselok i ill ii fii iliiz. 31k!.2@ i ie& g2i AlexandrovichKudryashov, Moskovskoi oblasti, ulitsa, Mira, 16, kv. 33, K li n;Stanislav Semenovich Rybin, poselok Khiminstituta, 3, kv. l8, Kalinin,all of U.S.S.R.

Primary ExaminerWilliam H. Short Assistant ExaminerL. M. PhynesAttorney-Waters, Roditi, Schwartz & Nissen ABSTRACT: An installation forthe continuous production of polycaproamide comprises the followingunits connected in series in the order given: a unit for meltingcaprolactam; a unit for mixing the molten caprolactam with an activatorand a stabilizer; a unit for continuous polymerization of caprolactam; aunit for distilling off low-molecular compounds; a unit for catalyticdecomposition of cyclic oligomers of caprolactam; and a unit forcondensation of low-molecular compounds.

PATENTED SEPZI 1971 3,607', 102

SHEET 2 OF 2 :mmm

APPARATUS FOR THE CONTINUOUS PRODUCTION OF POLYCAPROAMIDE The presentinvention relates to apparatus for the continuous production ofpolycaproamide which is used in the manufacture of manmade fibers andplastics.

A continuous method of producing polycaproamide is known, whereincaprolactam is melted and to it are added a molecular-weight stabilizercomprising an organic acid or derivative or an organic acid in an amountof 0.6 percent by weight of the caprolactam, and an activator, themolten caprolactam being polymerized and low-molecular compounds removedfrom the obtained melt of polycaproamide under vacuum over a periodoil-6 hours with subsequent condensation and filtration of saidlowmolecular compounds (cf. Jour. Chem. Engineering No.7, 1966).

A disadvantage of the known method is the high content of low-molecularcompounds in the polycaproamide obtained (3-3.5 percent by weight).

Another disadvantage of the known method is the deposition in thecondensation system of cyclic oligomers included in the low-molecularcompounds removed under vacuum, thus causing interruptions in theoperation of said condensation system, and consequently, of the entireinstallation.

Yet another disadvantage of the known method is the presence of theoperation of filtration of low-molecular compounds after theircondensation.

[t is an object of the present invention to provide apparatus forcontinuously producing polycaproamide making it possible to reduce thecontent of low-molecular compounds in the product polycaproamide to1.3-1.5 percent by weight, prevent the deposition of cyclic oligomers ofcaprolactam in the condensation system and eliminate the operation offiltering low-molecular compounds.

The above and other objects are achieved according to the invention bythe provision of apparatus for continuously producing polycaproamide,wherein an organic acid or its derivative is added to molten caprolactamin the amount of 0.65-2 percent by weight and low-molecular compoundsare distilled off under vacuum over a period of 8-16 hours.

In order to prevent the deposition in the condensation system of cyclicoligomers of caprolactam forming part of the low-molecular compounds,said oligomers are decomposed catalytically to monomer caprolactam undervacuum at a temperature of 240280 C. before condensation of saidlowmolecular compounds.

A known installation for the continuous production of polycaproamidecomprises a number of units connected in accordance with the flow sheet,viz: a unit for melting caprolactam, a unit for mixing moltencaprolactam with activator and stabilizer additions, a unit forcontinuous polymerization of caprolactam, a unit for distilling offlow-molecular compounds and a condensation system for the same (cf.Jour. Chem. Engineering No.7, 1966).

A disadvantage of the known installation is discontinuity in itsoperation due to clogging of the pipes of the condensation system by thedeposition of cyclic oligomers of caprolactam.

Another disadvantage of the known installation is the cumbersomeness ofthe condensation system which consists of an apparatus for condensinglow-molecular compounds, filters for coarse and fine purification of thecondensate, barometric receivers for caprolactam, and circulating pumps,said elements of the condensation system being connected by pipes.

With the object of the preventing the deposition of cyclic oligomers inthe condensation system and eliminating the stage of filtration oflow-molecular compounds, the installation of the present inventioncomprises means for melting caprolactam, means for mixing moltencaprolactam with activator and stabilizer additions, means forcontinuous polymerization of caprolactam, means operating under vacuumfor distilling off low-molecular compounds, and a means for condensingthe vapors of low-molecular compounds, all of said means being connectedin series with order given there being a means for catalyticdecomposition of cyclic oligomers of caprolactam mounted between themeans for distilling off low-molecular compounds and the means for theircondensation.

Said means for the catalytic decomposition of cyclic oligomers ofcaprolactam comprises a cylindrical tank filled with catalytic agent andheated by a liquid or vapor heating medium.

The invention will now be explained by a description of an embodimentthereof with reference to the accompanying drawings, wherein: 1

FIG. 1 diagrammatically shows an installation, according to theinvention, for applying the continuous production of polycaproamideincluding the stage of catalytic decomposition of cyclic oligomers ofcaprolactam; and

FIG. 2 diagrammatically shows a section through the apparatus forcatalytic decomposition of cyclic oligomers of caprolactam included inthe above installation.

The installation comprises apparatus 1 for melting caprolactam,apparatus 2 for mixing molten caprolactam with activator and stabilizeradditions, pumping-unit 3 connected by pipes to apparatus 1 and 2,apparatus 4 for continuous polymerization of caprolactam, pumping unit 5connected by pipes to apparatus 2 and 4, apparatus 6 for distillingoff'lowmolecular compounds, pumping unit 7 with gear pumps connected toapparatus 4 and 6, screw pump 8 connected to apparatus 6, apparatus 9for catalytic decomposition of cyclic oligomers of caprolactam connectedto apparatus 6 for distilling off low-molecular compounds, apparatus 10for condensing vapor of low-molecular compounds connected to apparatus 9for catalytic decomposition of cyclic oligomers of caprolactam and tobarometric receiver 11 for caprolactam and water.

The installation for application of the continuous production ofpolycaproamide operates in the following manner.

Caprolactam is melted in apparatus 1 which is heated with water and isprovided with a stirrer. The molten caprolactam is fed by pumping unit 3into apparatus 2 which is provided with a stirrerand where there areadded to the melt an activator, e.g. distilled water, and an organicacid or derivative of an organic acid as a molecular-weight stabilizer.

The amount of stabilizer is adjusted within the range of 0.62-2 percentby weight of the caprolactam.

The reaction mixture is then fed by pumping unit 5 into apparatus 4 forcontinuous polymerization where the caprolactam is polymerized in astream of nitrogen at a temperature of 250280C. The melt ofpolycaproamide thus obtained is fed by pumping unit 7 into apparatus 6for distilling off lowmolecular compounds wherein from a thin layer ofthe melt, water vapor, caprolactam and its cyclic oligomers are drivenoff over a period of 23-16 hours at a temperature of 260290 C. and avacuum of 2-5 mm. of mercury.

As a result of holding the melt under vacuum for a lengthy period oftime, caprolactam monomer is distilled off completely from thepolycaproamide. Simultaneously the process of blocking the terminalaminoand carboxy groups is practically completed, thus giving apolycaproamide melt in which the molecular weight remains unchanged fora lengthy period of time and the thermodynamic equilibrium betweenpolymer and monomer is not restored.

The demonomerized polycaproamide containing 1.34.5 percent oflow-molecular compounds by weight is discharged from apparatus 6 bymeans of screw pump 8 and is conveyed for processing into plastics orfor spinning into fiber.

The vapor of low-molecular compounds leaving apparatus 6 containing 97percent by weight caprolactam, 2 percent by weight cyclic oligomers and1 percent by weight water is passed into apparatus 9 which is packedwith granulated catalyst and where there takes place catalyticdecomposition of cyclic oligomers of caprolactam monomer.

The vapor of caprolactam and water leaving apparatus 9 is condensed inapparatus 10 from which the condensate is passed into barometricreceiver 11 and is subsequently regenerated.

The present continuous arrangement for producing polycaproamide can becarried out without the stage of decomposition of cyclic oligomers ofcaprolactam.

in that case the low-molecular compounds removed from the polycaproamidemelt in apparatus 6 are condensed in apparatus 10 and the condensatefiltered through coarse and fine filters (not shown in drawing) andpassed into the barometric receiver.

Conversion of the cyclic oligomers contained in the lowmolecularcompounds into caprolactam monomer is carried out in the catalyticdecomposition apparatus shown in FIG. 2.

The apparatus for catalytic decomposition of the cyclic oligomers ofcaprolactam comprises vertical cylindrical vessel 12 with conical topand bottom 13. The apparatus has a heating jacket 14 with inlet andoutlet pipes 15 and 16 for liquid or vapor heating medium. The apparatusis supplied with fitting 17 for charging and fitting 18 for dischargingcatalyst 19 and also inlet and outlet pipes 20 and 21 for low-molecularcompounds. When in operation the apparatus is filled with granulatedcatalyst.

The apparatus operates in the following manner.

A vapor mixture of caprolactam, cyclic oligomers and water is passedinto the apparatus through inlet pipe 20 and flows through the layer ofcatalyst 19, whereupon the cyclic oligomers are decomposed intocaprolactam monomer which passes out of the apparatus in vapor formthrough outlet pipe 21. The apparatus is operated continuously at atemperature of 240280 C. and a vacuum of 2-5 mm. of mercury.

The present invention will now be illustrated by the following exampleof the production of polycaproamide.

EXAMPLE A melt of caprolactam with the addition of 4 percent distilledwater and 0.7 percent benzoic acid by weight is polymerized for 18 hoursin a stream of nitrogen at a temperature of 260 C.

The polycaproamide thus obtained, which has a relative viscosity of 1.95in sulfuric acid, is passed into the apparatus for distilling offlow-molecular compounds. Distillation is carried out for 14 hours at atemperature of 265 C. and a vacuum of 2-5 mm. of mercury.

The low-molecular compounds distilled off are passed into the apparatusfor decomposition of cyclic oligomers and there said oligomers areconverted into caprolactam monomer at a temperature of 250 C. and avacuum of 2-5 mm. of mercury. The vapors of caprolactam and waterleaving said apparatus are cooled in the condenser and the condensatepassed into the barometric receiver from which it is taken forregeneration.

The polycaproamide obtained, which has a relative viscosity of 2.6 insulfuric acid and contains 1.3-l .5 percent lowmolecular compounds byweight, is sent to a spinning machine to be made into fiber or isprocessed into plastics.

Though the present invention has been described in accordance with apreferred embodiment, it will be understood by those skilled in the artthat there may be changes and modifications of the invention withoutdeparting from the spirit and scope thereof.

These changes and modifications are to be considered as falling withinthe spirit and scope of the invention as defined in the appended claims.

What we claim is:

1. An installation for the continuous production of polycaproamidecomprising means for melting caprolactam, means for mixing the moltencaprolactam with activator and stabilizer additions, means forcontinuous polymerization of caprolactam, means operating under vacuumfor distilling off low-molecular compounds, means for catalyticdecomposition of cyclic oligomers of caprolactam and means forcondensation of low-molecular compounds, all of said means beingconnected in series in the order given.

